1. Field of the Invention
The present invention relates to the area of cyclam dimers and, more particularly, relates to an improved process for preparing a specific pharmaceutically active 1,4-phenylene-bis-(methylene)-linked cyclam dimer.
2. Description of the Prior Art
U.S. Pat. No. 5,021,409 is directed to a method of treating retroviral infections comprising administering to a mammal in need of such treatment a therapeutically effective amount of a bicyclic macrocyclic polyamine compound. Although the usefulness of certain alkylene and arylene bridged cyclam dimers is generically embraced by the teachings of the reference, no arylene bridged cyclam dimers are specifically disclosed.
WO 93/12096 discloses the usefulness of certain linked cyclic polyamines in combating HIV and pharmaceutical compositions useful therefor. Among the specifically disclosed compounds is 1,1'-[1,4-phenylenebis-(methylene)]-bis-1,4,8,11 tetraazacyclotetradecane (and its acid addition salts), which compound is a highly potent inhibitor of several strains of human immune deficiency virus type 1 (HIV-1) and type 2 (HIV-2).
European Patent Appln. 374,929 discloses a process for preparing mono-N-alkylated polyazamacrocycles comprising reacting the unprotected macrocycle with an electrophile in a non-polar, relatively aprotic solvent in the absence of base. Although it is indicated that the monosubstituted macrocycle is formed preferentially, there is no specific disclosure which indicates that linked bicyclams can be synthesized by this process.
U.S. Pat. No. 5,047,527 is directed to a process for preparing a monofunctionalized (e.g., monoalkylated)cyclic tetramine comprising: 1) reacting the unprotected macrocycle with chromium hexacarbonyl to obtain a triprotected tetraazacycloalkane compound; 2) reacting the free amine group of the triprotected compound prepared in 1) with an organic (e.g., alkyl) halide to obtain a triprotected monofunctionalized (e.g., monoalkylated) tetraazacycloalkane compound; and 3) de-protecting the compound prepared in 2) by simple air oxidation at acid pH to obtain the desired compound. In addition, the reference discloses alternative methods of triprotection employing boron and phosphorous derivatives and the preparation of linked compounds, including the cyclam dimer 1,1'-[1,4-phenylenebis-(methylene)]-bis-1,4,8,11-tetraazacyclotetradecane, by reacting triprotected cyclam prepared as set forth in 1) above with an organic dihalide in a molar ratio of 2:1, and deprotecting the resultant compound to obtain the desired cyclam dimer.
J. Med. Chem., Vol. 38, No. 2, pgs. 366-378 (1995) is directed to the synthesis and anti-HIV activity of a series of novel phenylenebis(methylene)-linked bis-tetraazamacrocyclic analogs, including the known cyclam dimer 1,1'-[1,4-phenylenebis(methylene)]-bis-1,4,8,11-tetraazacyclotetradecane. The cyclam dimers disclosed in this reference, including the afore-mentioned cyclam dimer, are prepared by: 1) forming the tritosylate of the tetraazamacrocycle; 2) reacting the protected tetraazamacrocycle with an organic dihalide, e.g., dibromo-p-xylene, in acetonitrile in the presence of a base such as potassium carbonate; and 3) de-protecting the bis-tetraazamacrocycle prepared in 2) employing freshly prepared sodium amalgam, concentrated sulfuric acid or an acetic acid/hydrobromic acid mixture to obtain the desired cyclam dimer, or an acid addition salt thereof.
Although the processes disclosed in U.S. Pat. No. 5,047,527 and the J. Med. Chem. reference are suitable to prepare the cyclam dimer 1,1'-[1,4-phenylenebis-(methylene)]-bis-1,4,8,11-tetraazacyclotetradecane, they involve the use of cyclam as a starting material, a compound which is expensive and not readily available. Accordingly, in view of its potent anti-HIV activity, a number of research endeavors have been undertaken in an attempt to develop a more practical process for preparing 1,1'-[1,4-phenylenebis-(methylene)]-bis-1,4,8,11-tetraazacyclotetradecane.